Anomalies in the shape of the eye and specifically the shape as defined in part by the corneal can cause visual disorders. Hyperopia occurs when the eyeball is too short. In such a case, parallel rays from greater than 20 feet focus behind the retina. Myopia, on the other hand occurs when the eyeball is too long. The focus of parallel rays in this case is in front of the retina. Astigmatism is a condition in which the parallel rays of light do not come to a single point, but rather have a variable focus due to the fact that the cornea is aspherical and refracts light in a different meridian at different distances. Some degree of astigmatism is normal, but where it is too high, it must be corrected in order to provide acceptable vision.
Conditions such as hyperopia, myopia and astigmatism are usually corrected by glasses or contact lenses. Surgical methods for the correction of such disorders have been cited in the literature and include radial keratotomy (see e.g. U.S. Pat. Nos. 4,815,463 and 4,688,570) and laser corneal ablation (see e.g. U.S. Pat. No. 4,941,093). Further, the general method of implanting rings in the corneal stroma to change the curvature of the cornea is known. Previous work involving the implantation of polymethylmethacrylate (PMMA) rings, allograft corneal tissue and hydrogels is well documented. One of the ring devices involves a ring design that allows a split ring to be inserted into a channel. The channel is formed by dissecting the stromal layer of the cornea using a minimally invasive incision. Thereafter, the implant is inserted into the channel and the channel is sutured shut.
U.S. Pat. No. 4,452,235, which is herein incorporated by reference in its entirety, describes a method and apparatus for corneal curvature adjustment. The method involves inserting one end of a split end adjusting ring into the cornea of the eye and moving the ring in a circular path until its ends meet. The ends are thereafter adjusted relative to each other so that the ends can be connected. When so connected the shape of the eye will have assumed a desired curvature.
Various devices were required in order to facilitate the implantation of the rings of the type described in U.S. Pat. No. 4,452,235. Such a holder for inserting corneal curvature adjustable rings is described within U.S. Pat. No. 4,961,744 issued Oct. 9, 1990. Further, prior to inserting the ring it is necessary to cut an annular channel within the cornea and a device for cutting such a channel is disclosed within U.S. Pat. No. 4,766,895 issued Oct. 30, 1988.
Other devices for adjusting the corneal curvature have been disclosed such as the device shown within U.S. Pat. No. 4,671,276 issued Jun. 9, 1987. In addition, devices for affecting other parts of the eye such as an iris retaining device are disclosed within U.S. Pat. No. 4,782,820 issued Nov. 8, 1988 and a variable focus lens which is disclosed within U.S. Pat. No. 5,066,301 issued Nov. 19, 1991. More recently a method of changing cornea curvature by injecting a gel into the cornea was disclosed in U.S. Pat. No. 5,090,955 issued Feb. 25, 1992.
The present invention describes split ring devices which are inserted in the corneal stroma and have adjustable thicknesses which provide certain advantages and improvements as compared to earlier intrastromal corneal rings.